550 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



Used with other colors, they render the latter more perma- 

 nent, especially alkaline preparations. The varieties of 

 shade are not produced by mixtures, but by regulating the 

 temperature to which the color is exposed in the course of 

 manufacture. These colors attach themselves permanently 

 to the fibres, by the mere evaporation of the water in which 

 they are dissolved. They are all soluble in water, and are 

 precipitated by mineral as well as by organic acids. They 

 dye equally well silk, cotton, and linen. 



The method of dyeing is as follows: The colors are dis- 

 solved in hot water, and the goods are steeped and turned in 

 the solution from thirty to forty-five minutes ; they are next 

 fixed by a hot solution of bichromate of potash, in which 

 they are left for about fifteen minutes, washed with pure 

 water (in the case of wool and silk, to remove excess of al- 

 kali), and then placed in an alkaline bath made up with a 

 pound of soda to forty-seven quarts of water, and washed 

 finally with clear water. 1 A, October 16, 1874, ISO. 



TESTS FOR THE PRINCIPAL DYE-STUFFS IX COLORED FABRICS. 



The following course of examination has been suggested 

 by F. Fohl for ascertaining the dye-stuff employed in any 

 particular case in producing one of the five principal colors. 



I. Blue. Logwood, Prussian-blue, aniline-blue, and indigo 

 are chiefly to be considered. Proceed as follows : 



A. Cover a sample of the fabric, the color of which is to be 

 tested, with citric, or dilute hydrochloric, acid : 1. Change of 

 color to red or orange indicates logwood ; 2. No change of 

 color either Prussian-blue, aniline-blue, or indigo. B. Im- 

 merse another sample in a solution of chloride of lime: 1. No 

 change of color Prussian-blue ; 2. Decoloration, or a yellow- 

 ish coloration aniline-blue or indigo-blue ; to distinguish be- 

 tween these two, place another sample in caustic soda, when 

 decoloration, or change of color, will indicate aniline-blue, and 

 permanence of color indigo-blue. The presence of the blue 

 dye, indicated by the preceding tests, may be confirmed by the 

 following reactions. Logwood-blue is reddened by acids, and 

 restored by alkalies. The fabric yields a white or grayish 

 ash on incineration of the former color if the mordant was 

 alum, of the latter if it was blue vitriol; and in this latter 

 case the edge of the flame, during incineration, will also have 



